A newly published metal-on-metal hip replacement study is reporting that the majority of failures occur early, within two years of surgery. The study, published in the journal Orthopedics, is just the latest to indicate that close follow-up of metal-on-metal hip implant patients is warranted.
This new study reviewed data on 80 patients who underwent revision of a failed metal-on-metal total hip replacement for any reason at two high-volume revision institu¬tions. The revisions had occurred over 7 years between February 2003 and October 2010. The reasons for a metal-on-metal hip implant failure included:
• Aseptic acetabular loosening, 56% (45/80 patients)
• Infection, 12.5%
• Metal hypersensitivity, 6.25%
• Failed resurfacing, 6.25%
• Fracture, 5%
• Loose stem, 3.75%
• Dislodged liner, 3.75%
• Seizing, 1.25%
• Cup malposi¬tion, 1.25%
• femoral stem fracture, 1.25%
Most of the patients who experienced aseptic acetabular loosening had received either Zimmer’s Durom Cup (78% or 35/45 patients), or DePuy Orthopaedic’s ASR cup (9% or 4/35 patients), both of which had been named in recalls because of their high failure rates. Other cups that loosened included 2 (4.4%) Magnum cups (Biomet, Warsaw, Indiana), 2 (4.4%) Pinnacle cups (Depuy), 1 (2.2%) Conserve cup (Wright Medical, Arlington, Tennessee), and 1 (2.2%) un¬known cup.
Ten patients in total had significant metallosis or significantly involved local tissue changes due to the metal debris seen during revision surgery. These included 4 patients with ASR cups, 2 with Pinnacle, 2 with Magnum, 1 with the Birmingham Hip Resurfacing cup, and 1 with an unknown cup. Four of these patients failed due to asceptic loosening. Inspection of component position when aseptic loosening was ruled out demonstrated vertical and anteverted components in 2 patients and vertical and retroverted components in 2 patients. The remaining 2 patients, with the Birmingham and ASR cups, were revised for pseudotumor formation, after the masses were discovered via MRI following blood tests that revealed high metal ion levels.
According to the study, all of the metal-on-metal hip implants failed relatively early in the postoperative period, regardless of the reason for failure. Overall, 78% of the revisions were being performed within 2 years of the initial operation and 92.5% within 3 years.
Since the August 2010 recall of DePuy Orthopaedic’s ASR hip replacement, the entire class of metal-on-metal hip implants has come under scrutiny, as a number of studies have found evidence that that the devices can shed dangerous amounts of chromium and cobalt into patients’ bloodstreams. Last month, the U.S. Food & Drug Administration (FDA) revealed that it had received 16,800 negative event reports involving metal hips between 2000 and 2011. Of those, more than 14,000 involved revision surgeries, in which a defective implant was removed. Recently, FDA’s Orthopaedic and Rehabilitation Devices Panel recommended that metal-on-metal hip implant patients undergo regular monitoring to ensure their devices are not failing. The panel also called for new warning labels for all-metal hip implants, including warnings regarding their association with the development of pseudotumors and high levels of metal ions in patients’ blood.